TS6 errors due to ts-loader forcing deprecated compiler options

[devinant]

Current behavior

Running Cypress with TypeScript 6+ produces compiler errors about deprecated TypeScript options, even though these options are not defined in the project's tsconfig.json (i.e. they are injected)

Desired behavior

Cypress should not inject compilerOptions.downlevelIteration if the compilerOptions.target is set to es6 (https://www.typescriptlang.org/tsconfig/#downlevelIteration). Neither should cypress rely on "moduleResolution": "classic" (see https://www.typescriptlang.org/tsconfig/#moduleResolution)

Test code to reproduce

Minimal reproduction repository: https://github.com/devinant/cypress-ts6

Steps to reproduce:

npm install
npx cypress run --spec "cypress/e2e/1-getting-started/todo.cy.js"

The TypeScript deprecation errors will appear during the Cypress run and the tests won't run.

Cypress Version

10.15.0

Debug Logs

====================================================================================================

  (Run Starting)

  ┌────────────────────────────────────────────────────────────────────────────────────────────────┐
  │ Cypress:        15.10.0                                                                        │
  │ Browser:        Electron 138 (headless)                                                        │
  │ Node Version:   v20.19.0 (/Users/dino/.nvm/versions/node/v20.19.0/bin/node)                    │
  │ Specs:          1 found (todo.cy.js)                                                           │
  │ Searched:       cypress/e2e/1-getting-started/todo.cy.js                                       │
  └────────────────────────────────────────────────────────────────────────────────────────────────┘


────────────────────────────────────────────────────────────────────────────────────────────────────

  Running:  todo.cy.js                                                                      (1 of 1)

Oops...we found an error preparing this test file:

  > cypress/support/e2e.ts

The error was:

Error: Webpack Compilation Error
[tsl] ERROR
      TS5101: Option 'downlevelIteration' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.

[tsl] ERROR
      TS5107: Option 'moduleResolution=classic' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.

[tsl] ERROR
      TS5101: Option 'downlevelIteration' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.

[tsl] ERROR
      TS5107: Option 'moduleResolution=classic' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.

[tsl] ERROR
      TS5101: Option 'downlevelIteration' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.

[tsl] ERROR
      TS5107: Option 'moduleResolution=classic' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
    at handle (/Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-preprocessor/dist/index.js:296:23)
    at finalCallback (/Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/webpack/lib/Compiler.js:500:32)
    at /Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/webpack/lib/Compiler.js:578:17
    at /Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/webpack/lib/HookWebpackError.js:67:2
    at Hook.eval [as callAsync] (eval at create (/Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
    at Hook.CALL_ASYNC_DELEGATE [as _callAsync] (/Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/tapable/lib/Hook.js:18:14)
    at Cache.storeBuildDependencies (/Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/webpack/lib/Cache.js:126:37)
    at /Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/webpack/lib/Compiler.js:574:19
    at Hook.eval [as callAsync] (eval at create (/Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
    at Hook.CALL_ASYNC_DELEGATE [as _callAsync] (/Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/tapable/lib/Hook.js:18:14)
    at /Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/webpack/lib/Compiler.js:570:23
    at Compiler.emitRecords (/Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/webpack/lib/Compiler.js:1046:4)
    at /Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/webpack/lib/Compiler.js:560:11
    at /Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/webpack/lib/Compiler.js:1009:14
    at Hook.eval [as callAsync] (eval at create (/Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
    at Hook.CALL_ASYNC_DELEGATE [as _callAsync] (/Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/tapable/lib/Hook.js:18:14)
    at /Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/webpack/lib/Compiler.js:1006:27
    at /Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/neo-async/async.js:2818:7
    at done (/Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/neo-async/async.js:3522:9)
    at alreadyWritten (/Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/webpack/lib/Compiler.js:811:8)
    at /Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/webpack/lib/Compiler.js:922:17
    at /Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/node_modules/graceful-fs/graceful-fs.js:123:16
    at /Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/graceful-fs/graceful-fs.js:123:16
    at /Users/dino/Library/Caches/Cypress/15.10.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/graceful-fs/graceful-fs.js:123:16
    at FSReqCallback.readFileAfterClose [as oncomplete] (node:internal/fs/read/context:68:3)

This occurred while Cypress was compiling and bundling your test code. This is usually caused by:

- A missing file or dependency
- A syntax error in the file or one of its dependencies

Fix the error in your code and re-run your tests.

  (Results)

  ┌────────────────────────────────────────────────────────────────────────────────────────────────┐
  │ Tests:        0                                                                                │
  │ Passing:      0                                                                                │
  │ Failing:      1                                                                                │
  │ Pending:      0                                                                                │
  │ Skipped:      0                                                                                │
  │ Screenshots:  0                                                                                │
  │ Video:        false                                                                            │
  │ Duration:     0 seconds                                                                        │
  │ Spec Ran:     todo.cy.js                                                                       │
  └────────────────────────────────────────────────────────────────────────────────────────────────┘


====================================================================================================

Other

Temporary workaround:

{
  "compilerOptions": {
+   "ignoreDeprecations": "6.0",
    "target": "es6",
    "lib": ["es6", "dom"],
    "sourceMap": true,
    "types": ["cypress", "node"]
  }
}

I'm aware that TS6 is currently in beta and this may not be officially supported. If this is expected behaviour while TS6 is still in beta, please feel free to close the issue :). I just wanted to provide a minimal reproduction in case it is helpful.

Thanks!

[MikeMcC399]

@devinant

The TypeScript 6 beta was announced on Feb 11, 2026 and includes a list of Breaking Changes and Deprecations.

Although the Cypress TypeScript documentation states:

To use TypeScript with Cypress, you will need TypeScript 5.0+.

that would not include a TypeScript 6 beta, and I would assume that the documentation will need to be updated after TypeScript 6 becomes officially released.

You can wait and see what the Cypress.io team says, or simply submit a new Feature Request for Cypress to support TypeScript 6 which would be a more generic placeholder for support changes necessary due to the breaking changes introduced in TypeScript 6.

[MikeMcC399]

Documentation PR cypress-io/cypress-documentation#6376 submitted

[devinant]

@MikeMcC399 you have a point. We're in agreement. Thanks for submitting the PR which clarifies what is supported.

[MikeMcC399]

https://docs.cypress.io/app/tooling/typescript-support#Install-TypeScript has been modified to now state:

To use TypeScript with Cypress, you will need TypeScript 5.x.

This should make it clear that TypeScript 6 is not (yet) supported.